For a 30mm drop, as people said I also suggest just dampers + springs, as these cheaper coilovers work better lower, because when they are higher as their preload is dependent on the height, they ride so rubbishly! When they are lower (when preload isn't crazy) they ride so much better.
Try looking for a used set to save money mate, most good ones last well if not slammed over speed bumps lol.
Is it 40mm on the rear as well Andy? What make springs?
Are the BMW struts?
Has any one had any experiance of H&R lowering springs?
The yanks seem to love them.
ECP don't do Eibachs it seems, but do sell H&R.....
Just took some pictures, arch gap is about 30mm on the rear, and about 50mm at the front, assuming I have measured it the right way?